Comments for Molecules and Madnesshttps://qchem.wordpress.com
An insight into the mind of a quantum chemist and computer geekFri, 08 Apr 2016 10:08:50 +0000hourly1http://wordpress.com/Comment on Canon Pixma ip4200 by rosalindryan2219https://qchem.wordpress.com/2006/03/13/canon-pixma-ip4200/#comment-51
Fri, 08 Apr 2016 10:08:50 +0000http://qchem.wordpress.com/2006/03/13/canon-pixma-ip4200/#comment-51LOL!! several WTF’s a moment!! Wtas happening? I hope everything is fine.https://ameo.link/rosalindryan221908180
]]>Comment on Intel Powerbooks by ertyuykiulohttps://qchem.wordpress.com/2005/11/14/intel-powerbooks/#comment-10
Wed, 09 Aug 2006 12:00:35 +0000http://qchem.wordpress.com/2005/11/14/intel-powerbooks/#comment-10Here are some links that I believe will be interested
]]>Comment on Google Mars by golfcarttoyzhttps://qchem.wordpress.com/2006/03/13/google-mars/#comment-9
Mon, 10 Jul 2006 03:42:11 +0000http://qchem.wordpress.com/2006/03/13//#comment-9I have to admit, I am not into Astronomy, but all of God’s great creations do fascinate me.
]]>Comment on What is an orbital? by Garethhttps://qchem.wordpress.com/2005/11/22/what-is-an-orbital/#comment-8
Tue, 29 Nov 2005 12:50:06 +0000http://qchem.wordpress.com/2005/11/22/what-is-an-orbital/#comment-8I agree with the definition that an orbital is a function which describes the properties of a single electron. I think that what I was trying to get at by starting with hydrogen (and hydrogen-like systems, I suppose), was that; because hydrogen-like atoms are the only systems with exact analytic solutions, then only they have orbitals which can be exactly defined. It is orbitals of this type that are used when attempting to qualitatively describe electronic structure or reaction mechanisms, involving multi-electron atoms, to a more general audience. The approximation arises due to the lack of exact solutions in such cases. I hope that clarifies my position a bit.

Also I agree that the Gaussian-type basis functions used in calculations are
chosen for the ease of evaluating the necessary integrals, but contractions of a number of such functions are often used in order to better approximate the Slater-type functions as found in the exact hydrogen-like solutions. Pretty sure this is true for the standard Pople sets, n-31G etc, not sure at all for others. Any thoughts?

]]>Comment on Open Source QC packages by qchemhttps://qchem.wordpress.com/2005/11/10/open-source-qc-packages/#comment-7
Tue, 29 Nov 2005 10:28:01 +0000http://qchem.wordpress.com/2005/11/10/open-source-qc-packages/#comment-7Hybrid DFT usually reduces me to shaking my head (and muttering something about a lack of rigour), but I should really accept that it’s currently the way forward and try out some of the OSS packages – I’ll try and track some down.

Thanks for pointing that out.

]]>Comment on What is an orbital? by qchemhttps://qchem.wordpress.com/2005/11/22/what-is-an-orbital/#comment-6
Tue, 29 Nov 2005 10:20:28 +0000http://qchem.wordpress.com/2005/11/22/what-is-an-orbital/#comment-6The answer I thought up to the question as I was asking it was something along the lines of “a wavefunction that describes a single particle, namely an electron”.

This is in essence very similar to Geoff’s description (practically identical when you think about it), but I don’t remember anyone ever teaching me this, certainly not at the undergraduate level [although there is the chance I simply wasn’t listening (asleep/dead)]. It seems to be assumed knowledge at the university level but I feel some explanation (just like the one-liners we’re discussing here) is probably warranted after the somewhat poor responses I’ve recieved from PhD students.

]]>Comment on What is an orbital? by Geoffhttps://qchem.wordpress.com/2005/11/22/what-is-an-orbital/#comment-5
Mon, 28 Nov 2005 20:38:10 +0000http://qchem.wordpress.com/2005/11/22/what-is-an-orbital/#comment-5I disagree somewhat with Gareth. You first describe an atomic orbital, based on a hydrogen atom.

That’s not quite right.

Here’s my definition, just for kicks. “An orbital is a one-electron solution to a given Schrodinger equation describing a system.” In short, it’s one eigenfunction from the given Schrodinger equation. That’s it. Add interpretation if you wish, but caveat lector.

Molecular orbitals in theory could be derived from one-electron hydrogenic orbitals as you’ve described. Certainly that’s how we teach it in “general chemistry” classes. But in practice, we don’t use exact hydrogenic orbitals for the electronic structure of multi-electron atoms or molecules. We use some arbitrary basis set functions to describe those because it’s more computationally efficient.

]]>Comment on What is an orbital? by Garethhttps://qchem.wordpress.com/2005/11/22/what-is-an-orbital/#comment-4
Fri, 25 Nov 2005 15:46:20 +0000http://qchem.wordpress.com/2005/11/22/what-is-an-orbital/#comment-4The concept of an orbital seems to be one of those things that we have an intuitive grasp of; we have a feeling for what they represent, we can use them to predict the nature of reaction mechanisms; but when it comes to an accurate description of what one is, we stumble. (I find myself in a similar situation when trying to explain logarithms tothe uninitiated). Here is my attempt, hopefully, if I stumble, I won’t fall flat on my face:

An orbital is a exact solution to the Schrodinger equation for the hydrogen atom, from which descriptions of the motion (extracted by operators) and spatial distribution (related to the square of the orbital/wavefunction) of its electron at a particular energy level can be extracted. It is approximated that electronic structure of multi-electron atoms can described by associating each electron to functions of the same type (in terms of symmetry) as found in the hydrogen atom. It is further approximated that the electronic structure of molecules can be described by a linear combination of these approximate atomic orbitals, producing molecular orbitals with spatial distribution localised to one or two of the constituent atoms or delocalised to occupy space in the proximity of a large number of atoms.

]]>Comment on Open Source QC packages by geoffhhttps://qchem.wordpress.com/2005/11/10/open-source-qc-packages/#comment-3
Fri, 11 Nov 2005 00:25:06 +0000http://qchem.wordpress.com/2005/11/10/open-source-qc-packages/#comment-3I don’t think Gaussian will ever really go open source. A company that bans various academic departments because a group there works on a competing program is unlikely to change their mind anytime soon. Their license is very strange — you can’t talk about performance of Gaussian on different hardware or compare it to other programs.

BTW, while I like both MPQC and PyQuante, they’re not the only open source first principles codes, particularly if you’re open to DFT-only programs.

Both MPQC and PyQuante are nice examples, but I’d really like to see some of the open source programs add semiempirical theory (v. important for large systems) and start to work together (e.g., common formats for wavefunctions, “cube” files, etc.)

Certainly the cheminformatics open source projects already are. See http://blueobelisk.org/ for example. I’ve also gotten good feedback through Open Babel and the Computational CML projects — but it may take a little while.

]]>Comment on Printing pdf’s by somethinghttps://qchem.wordpress.com/2005/11/01/printing-pdfs/#comment-1
Tue, 01 Nov 2005 17:36:27 +0000http://qchem.wordpress.com/2005/11/01/printing-pdfs/#comment-1it’s not just PDF documents. You should reconsider the level of trust you place in anything Adobe puts out. The only Adobe app that I truly love is InDesign CS/CS2.
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